John Calvin Commentary Psalms 78:34

"When he slew them, then they inquired after him; And they returned and sought God earnestly." — Psalms 78:34 (ASV)

When he slew them, then they sought him. By the circumstance recorded here, it is intended to aggravate their guilt. When, under a conviction of their wickedness, they acknowledged that they were justly punished, and yet did not with sincerity of heart humble themselves before God, but rather mocked him, intending to appease him with false pretenses, their impiety was all the more inexcusable.

If a man who has lost his judgment does not feel his own calamities, he is excusable because he is unfeeling. But he who is forced to acknowledge that he is guilty, and yet always continues the same, or after having superficially sought pardon with fair but deceitful words, suddenly returns to his former state of mind, clearly shows by such hollowness of heart that his disease is incurable.

It is subtly implied here that the punishments by which such an obstinate people were compelled to seek God were of no common or ordinary kind. And we are informed (verse 35), not only that they were convinced of their wickedness, but also that they were affected by a sense and remembrance of the redemption from which they had fallen.

By this means, they are even more effectively deprived of all excuse on the grounds of ignorance. The language implies that they were not carried away unintentionally or deceived through ignorance, but that they had provoked the wrath of God by dealing treacherously, as it were, with deliberate purpose. And, indeed, God opened their eyes in order to more clearly expose their desperate wickedness, as if, shaking off their hypocrisy and flatteries, he drew them from their hiding places into the light.